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Phys. Unit 4

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Central nervous system components   spinal cord and brain  
What nervous system is divided into   central and peripheral systems  
peripheral nervous system components   afferent and efferent  
How much of the blood is in the brain/   15-20% of total blood supply  
Weight of brain and percent of total body weight   1.5 kg and about 2% of weight of 70 kg man  
What secretes cerebrospinal fluid?   choroid plexuses  
What is the blood-brain barrier?   A tissue complex made by the ependyma neuroglia and controls rates of entry and types of substances allowed in  
Direction of afferent NS?   Sensory organs to CNS  
Direction of efferent NS?   CNS to Motor organs  
Myelination description   Schwann cells secrete mylin (fat) sheath around axon that insulates the axon and increases velocity of transmission of impulses; have Nodes of Ranvier  
Two types of NS cells   Neurons and neuroglia  
What is basic communication unit of NS?   Neuron  
Part of neuron that receives stimulus   Dendrites  
What synthesizes proteins and neurotransmitters?   Cell body  
Where is the action potential initiated?   In the cell body in the initial segment, or Hillock Area  
Most common type of neuron   interneurons (200,000)  
Least common type of neuron   afferent (1.0)  
Afferent neuron size   long dendrites, short axons  
Efferent neuron size   short dendrites, long axons  
Interneurons size   short dendrites, and either long or short axons  
Number of neurons and neuroglia   neurons- 10% neuroglia- 90%  
Size of neurons and neuroglia   neuroglia are smaller, neurons are larger volume is occupied in 50/50 neurons/neuroglia  
Somatic Division definition   only skeletal muscles (voluntary) activities; fast transmission; always excitatory; uses ACH  
Transmission at synapse   most chemical (neurotransmitter), a few electrical  
Synapses definition   1. can be excitatory(facilitatory) or inhibitory 2. inputs (divergent and convergent)  
How many synapses does a spinal neuron have?   15 x 10^3  
How many synapses does a cranial neuron have?   100 x 10^3  
Autonomic Division definition   involuntary activities; parasympathetics and parasympathetics; innervates smooth, cardiac muscles; uses 2 neurons and ganglion; uses ACH and norepinephrine  
What division is the major controller of homeostasis?   autonomic division  
What is the name for adrenal secretions?   neurohormones  
Adrenal Medulla secretions?   20%- norepinephrine 80%- epinephrine  
Sympathetic division secretions?   20%- epinephrine 80%- norepinephrine  
Cholinergic receptors   1. Nicotinic: respond to nicotine; found on other neurons and skeletal muscle 2. muscarinic- respond to mushroom toxin; found on smooth and cardiac muscle, as well as glands  
What binds cholinergic receptors?   ACH  
Adrenergic receptors   1. Alpha- excitatory or stimulatory 2. Beta- inhibitory  
What binds to adrenergic receptors?   epinephrine or norepinephrine(does not bind to beta receptors)  
Exceptions to receptors   Cardiac muscle-norepinephrine binds to beta receptors (excitatory response) **(NE is not supposed to bind to beta receptors and not excitatory)  
Resting membrane potential (Vm)   -70 mV  
Depolarization definition   1. Apply excitatory stimulus 2. Na channels open and K channels close 3. Na influx and cell becomes more positive (30-40 mV)  
Repolarization definition   1. K channels open, Na channels closed 2. K efflux and cell becomes more negative (-80 mV)  
Hyperpolarization definition   1. Apply an inhibitory stimulus 2. K channels open, Na channels close 3. K effux, cell becomes more negative than resting potential (Vm)  
Threshold value   -55 mV  
Equilibrium potential values   1. K+: -90 mV (more inside cell) 2. Na+: +60 mV (more outside cell) 3. Cl-: -70 mV (do not contribute to membrane signals)  
Types of potentials   graded and action  
Graded potential   1. created by subthreshold stimulus 2. amplitude/size depends on strength of stimulus 3. transmitted decrementally 4. useful in local or short distances 5. can be summed up to make an action potential  
Action potential   1. characteristic of excitable membranes-neurons, muscles, glands 2. caused by rapid changes using voltage-sensitive ion channels  
Threshold voltage value   +15 mV  
Magnitude or size of AP determined by what?   independent of stimulus strength, but determined by number of Action Potentials fired/unit of time  
Refractory periods   1. Absolute: during all of the depolarization and part of repolarization phase 2. Relative: during late part of the repolarization; can restimulate with supra-threshold stimulus only)  
Where is summation of a signal done on a neuron?   Hillock area because it has the lowest threshold value  


   





 
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Created by: kcapland on 2012-02-21



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